Pyrolysis systems

ABSTRACT

Systems and methods are disclosed for pyrolysis of waste feed material. Some systems include a main retort and a secondary retort. Syngas is produced by pyrolysis in the main retort, and is then mixed with combustion air and ignited, in some cases to produce energy. Carbon char travels to the secondary retort and is exhausted from the system through an airlock.

RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 15/196,645, filed Jun. 29, 2016, which is a continuation applicationof U.S. application Ser. No. 14/105,832, filed Dec. 13, 2013, now U.S.Pat. No. 9,394,484, granted on Jul. 19, 2016, the entire contents ofwhich are hereby incorporated by reference.

FIELD OF INVENTION

The present invention relates to systems and methods for pyrolyzingwaste materials and recovering heat from the pyrolysis process.

BACKGROUND

Waste materials present ever-increasing disposal problems.

In the past, refuse and toxic waste were often burned. However, due toincreased governmental and regulatory standards, the potential publichealth impacts of carcinogenic air emissions, such as dioxins andfurans, and the risks of spreading toxic plumes, the burning of wasteshas generally been abandoned.

Efforts have been made to replace burning of waste with pyrolysisprocesses that would provide for safe combustion with minimal emissionsand allow recovery of heat from combustion.

U.S. Pat. No. 6,758,150, the full disclosure of which is incorporatedherein by reference, describes a system for pyrolysis of waste material.The system includes a pyrolysis unit, a thermal oxidizer unit, and astack unit. The pyrolysis unit includes a first retort disposed within acombustion chamber and a second retort disposed outside the combustionchamber. The combustion chamber supplies heat, which pyrolyzes the wastematerial as it is conveyed through the first retort. The thermaloxidizer oxidizes pyrolysis gases from the first retort and the stackunit provides a draft to move the pyrolysis gases through the thermaloxidizer. Flue gases from the combustion chamber are vented toatmosphere.

SUMMARY

The present disclosure features improved pyrolysis units for use inpyrolysis systems that include a pyrolysis unit, a thermal oxidizerunit, and a stack unit, e.g., of the type described in U.S. Pat. No.6,758,150. As discussed above, in the pyrolysis systems disclosedherein, syngas is exhausted from the pyrolysis unit in a manner thatprevents formation of clinkers in the exhaust duct, and flue gases aredischarged from the pyrolysis unit in a manner that recovers their heatand eliminates discharge of flue gas to the environment. These and otherfeatures of the pyrolysis units enhances their viability for use incommercial processes and may increase energy yield from pyrolysissystems including the pyrolysis units.

In one aspect, the invention features a pyrolysis device comprising (a)a combustion chamber containing one or more burners configured togenerate hot flue gases; (b) a main retort, disposed within thecombustion chamber, configured to at least partially pyrolyze afeedstock delivered to the retort, thereby generating syngas; and (c) amixing chamber, into which the syngas and flue gases flow.

Some implementations may include one or more of the following features.

The device may further include (d) a flue gas relief duct having a firstend in sealing fluid communication with the combustion chamber and asecond end in fluid communication with the mixing chamber; and (e)disposed within the flue gas relief duct, a syngas relief duct having afirst end in fluid communication with the main retort and a second endin fluid communication with the mixing chamber. In some implementations,during use, the temperature of the gases within the flue gas relief ductand the syngas relief duct is within +/−25 degrees F. of the temperatureof the flue gas and syngas in the combustion chamber and main retort,respectively. The clearance between an outer wall of the syngas reliefduct and an inner wall of the flue gas relief duct may be selected suchthat the flow rate of the gases during use is about 30 to 60feet/second.

In some cases, a long axis of the syngas relief duct is disposedgenerally perpendicular to a horizontal plane taken through a long axisof the main retort. The long axis of the flue gas relief duct ispreferably also disposed generally perpendicular to the horizontalplane, in which case the long axes of the two ducts may be generallycolinear.

The device may further include a mixing baffle and distribution conewithin the mixing chamber, configured to direct gas outwardly within themixing chamber. The device may also include a combustion gas inlet andan afterburner element positioned downstream of the distribution cone.

The device may also include a thermal oxidizer chamber in fluidcommunication with the mixing chamber, and an afterburner systemdisposed within the thermal oxidizer chamber, and, in some cases, anexpansion chamber in fluid communication with the thermal oxidizerchamber. A plurality of mixing baffles may be disposed within theexpansion chamber. A blower may be disposed downstream of the expansionchamber, the blower being configured to draw a vacuum on the expansionchamber, thermal oxidizer chamber, and mixing chamber.

The device may also include a secondary retort in fluid communicationwith the retort and configured to receive solid residues from the mainretort. The secondary retort is preferably mounted on expansion rollersto allow relative movement of the main retort and secondary retort. Thismounting technique allows the secondary retort and main retort to beconnected by a rigid conduit.

In another aspect, the invention features methods of utilizing thedevices disclosed herein. For example, the invention features a methodcomprising (a) delivering a feedstock to a main retort that is disposedwithin a combustion chamber containing one or more burners; (b)utilizing the burners to generate hot flue gases and thereby at leastpartially pyrolyze the feedstock, generating syngas; and (c) drawing theflue gases and syngas into a mixing chamber by applying a negativepressure to the main retort and combustion chamber.

Some implementations of the method may include one or more of thefollowing features.

The method may further include (d) exhausting the flue gases from thecombustion chamber through a flue gas relief duct having a first end insealing fluid communication with the combustion chamber and a second endin fluid communication with the mixing chamber; and (e) exhausting thesyngas from the main retort through a syngas relief duct disposed withinthe flue gas relief duct, the syngas relief duct having a first end influid communication with the main retort and a second end in fluidcommunication with the mixing chamber.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a pyrolysis unit according to oneimplementation of the invention.

FIG. 2 is a schematic diagram of an expansion chamber in fluidcommunication with the pyrolysis unit shown in FIG. 1.

DETAILED DESCRIPTION

A pyrolysis unit 10 is shown in FIG. 1. Pyrolysis unit 10 may be used toperform the initial pyrolysis step in a pyrolysis system that includes athermal oxidizer unit and stack unit (not shown.) As noted above, thepyrolysis unit routes syngas discharge in a manner that reducesmaintenance of the unit, routes flue gases in a manner that recoverstheir heat and eliminates discharge of flue gas to the environment, andincludes other features which enhance the commercial viability of thepyrolysis system.

The pyrolysis unit 10 includes a combustion chamber 12, which is madefrom materials capable of withstanding temperatures of 1200-2600° F.Burners 14 are positioned within the combustion chamber. These burnersmay be natural gas or propane-fired and are adapted to generate andsupply hot combustion gases into the combustion chamber. While twoburners are illustrated, more or fewer could be provided.

A main retort 16 is disposed within the combustion chamber 12. Pyrolysisof the feed material takes place in this main retort, producingpyrolysis gases, referred to herein as syngas. The main retort 16includes slots or other openings (not shown) in its upper surface, whichare in fluid communication with a syngas conduit 17. The main retort hasa generally cylindrical cross section and contains a conveying elementconfigured to convey a feedstock through the retort, shown in FIG. 1 asscrew 18. The main retort 16 has a feed end 20 and a discharge end 22.The feed end and discharge end of the retort extend through the proximaland distal ends, respectively, of the combustion chamber 12. The screw18 is adapted to be axially rotated to move material from the feed endto the discharge end of the retort.

Feedstock is delivered to the main retort at the feed end 20. If thefeedstock is a solid material such as, for example, pieces of shreddedtire rubber, the feedstock is fed into a solid inlet 24, which may havea funnel (not shown) to retain the feedstock and direct it into anairlock 26. The funnel may include a level sensor to regulate deliveryof feedstock to the main retort for enhanced process control. Thepyrolysis unit may also include a liquid feed (not shown). Airlock 26regulates delivery of the feedstock into the main retort and is adaptedto prevent or minimize the admission of oxygen into the main retort. Thestructure of a suitable airlock is described in detail in U.S. Pat. No.6,758,150.

As the rotating screw 18 conveys the feedstock along the length of themain retort 16 in the direction of the arrow in FIG. 1, the feedstock issubjected to the heat from the burners 14 and to hot combustion gasesswirling about the main retort, pyrolyzing the material and generatingsyngas.

This syngas is exhausted (vertical arrow, FIG. 1) through a syngasrelief duct 28 in sealed fluid communication with the outlet of thesyngas conduit 17. The syngas relief duct is maintained at a negativepressure to draw syngas from the main retort. The syngas relief duct 28extends vertically from the main retort, and is preferably disposedgenerally perpendicular (within +/−10 degrees of perpendicular) to ahorizontal plane taken through the long axis of main retort, as shown.While it is preferred that the syngas relief duct be generallyperpendicular to the axis, in some implementations it can be within+/−45 degrees, e.g., within +/−20 degrees of vertical. The syngas reliefduct 28 is disposed within a flue gas relief duct 30 that is in sealedfluid communication with the combustion chamber 12. The hot flue gasesin the combustion chamber, generated by burners 14, are exhausted fromthe combustion chamber through the flue gas relief duct 30, keeping thesyngas warm as it travels through the syngas relief duct 28. Thetemperature of the flue gas and the syngas in their respective chambersis relatively close to the temperature of these gases in the combustionchamber, e.g., within +/−25° F. This reduces or eliminates the formationof solid residue (“clinker”) in the syngas relief duct, minimizingmaintenance. The generally vertical position of the syngas relief ductalso helps to keep the duct clear by causing any fines to drop back intothe main retort rather than being trapped in the duct.

The clearance between the walls of the two ducts, and the volumes of theducts, is selected to maintain a flow rate of from about 30 to 60feet/sec for both gases.

The flue gas then flows into a mixing chamber 32 where it mixes with thesyngas, rather than being exhausted to atmosphere. As a result, the heatenergy from the flue gas is recovered, enhancing the energy yield of thesystem. Moreover, emission of hot gases, and potentially particulate,from the pyrolysis unit to the environment is eliminated, improvingenvironmental compliance of the system.

Mixing of the syngas and flue gas is assisted by a mixing baffle 34,after which the gaseous mixture is distributed outwardly by adistribution cone 36. Distribution cone 36 forces the mixture outwardlywithin the mixing chamber as the mixture flows past combustion air inlet38. As it passes the combustion air inlet, the syngas/flue gas mixtureis further mixed with combustion air. The mixture of the three gasesthen enters thermal oxidizer chamber 42 where it passes throughafterburner burners 40. This routing of the gas mixture causes themixture to pass through the afterburner burners, igniting the gases. Thecombustion air inlet 38 is preferably positioned just upstream of theafterburner burners 40, as shown, rather than further upstream, toprevent pre-ignition of the gases. In some embodiments, the combustionair inlet is in the form of a ring surrounding the chamber 42.

Referring to FIG. 2, after passing through the afterburner burners 40,the gas mixture flows into an afterburner expansion chamber 42 whichincludes a plurality of mixing baffles 43 which tumble and mix the gas,giving the gas time to be completely or substantially completelycombusted and thereby reducing emissions from the system. The gasmixture then travels through a blower 45, which imposes a negativepressure on the thermal oxidizer chamber and combustion air inlet, andmay be exhausted to a stack. In some implementations, the pyrolysissystem may include an apparatus for recovering energy from the syngasand flue gas. For example, the discharge from the thermal oxidizer unitmay be supplied to a boiler where water is heated to produce steam. Thisand other methods of heat recovery from pyrolysis are well known, andare discussed, e.g., in U.S. Pat. No. 6,758,150.

The solid material that remains after pyrolysis of the feedstock in themain retort (carbon char) falls though a conduit 44 at the discharge endof the main retort into the feed end 46 of a secondary retort 48, whichis disposed outside of the combustion chamber 12 and directly below themain retort. As it passes through the secondary retort 48, conveyed by ascrew 50, the solid material cools, allowing it to be safely exhaustedwithout danger of ignition. Some further pyrolysis may also take placein the secondary retort, due to residual heat in the solid material.

To provide for thermal expansion of the conduit 44, and for relativemovement between the main retort 16 and secondary retort 48 due todifferential thermal expansion, thermal expansion rollers 52 may beprovided both at the end of the main retort adjacent the transition tothe secondary retort and below and supporting the secondary retort, asshown. These thermal expansion rollers provide for a degree of verticaland lateral movement between the main and secondary retort segments. Thethermal expansion rollers are supported on a framework (not shown.)

Near the discharge end of the secondary retort is a discharge 54including a discharge airlock 26. Material conveyed to the discharge 54by the screw 50 is discharged from the pyrolysis unit 10 through theairlock 26 into a suitable container. The length of the secondary retortis selected so that by the time the solid material is dischargedpyrolysis of the material is substantially complete and the material hascooled, preferably to a temperature of less than about 220° F.

Various sensors may be provided to control the operation of thepyrolysis system, as is well known.

The systems and methods disclosed herein are adapted to destroy mostforms of organic waste material, e.g., solid waste, liquid waste,hazardous waste, industrial wastes, and all forms of volatile organiccompounds (VOCs). The systems and methods can be used to processhydrocarbons, PCB's, rubber, chlorides, herbicides, pesticides,plastics, wood and paper. The pyrolysis process breaks down the wastematerial into gas and carbon char. The carbon char may be recycled foruse in any application that utilizes carbon, for example in inks orpaints, as activated carbon, in tires, and many other products.

Other Embodiments

A number of embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made without departing fromthe spirit and scope of the disclosure. Accordingly, other embodimentsare within the scope of the following claims.

What is claimed is:
 1. A method comprising: delivering a feedstock to amain retort that is disposed within a combustion chamber containing oneor more burners; utilizing the burners to generate hot flue gases andthereby at least partially pyrolyze the feedstock, generating syngas;exhausting the flue gases from the combustion chamber through a flue gasrelief duct that is separate from the combustion chamber and has a firstend in sealing fluid communication with the combustion chamber and asecond end in fluid communication with the mixing chamber; exhaustingthe syngas from the main retort through a syngas relief duct; anddrawing the flue gases and syngas through the respective ducts into amixing chamber by applying a negative pressure to the main retort andcombustion chamber.
 2. The method of claim 1 wherein the syngas reliefduct is disposed within the flue gas relief duct, the syngas relief ducthaving a first end in fluid communication with the main retort and asecond end in fluid communication with the mixing chamber.
 3. The methodof claim 1 wherein a long axis of the syngas relief duct is disposedgenerally perpendicular to a horizontal plane taken through a long axisof the main retort.
 4. The method of claim 3 wherein a long axis of theflue gas relief duct is also disposed generally perpendicular to thehorizontal plane.
 5. The method of claim 1 further comprising a mixingbaffle and distribution cone within the mixing chamber, configured todirect gas outwardly within the mixing chamber.
 6. The method of claim 5further comprising a combustion gas inlet and an afterburner elementpositioned downstream of the distribution cone.
 7. The method of claim 1further comprising a blower configured to draw a vacuum on the mixingchamber.
 8. The method of claim 1 wherein the clearance between an outerwall of the syngas relief duct and an inner wall of the flue gas reliefduct is selected such that the flow rate of the gases within the ductsis from about 30 to 60 feet/second.